Degradation of digital sources

A. Vivaldi

A. Vivaldi

Audioholic
<font color='#000000'>We often hear about the degradation of analog but what about digital? I've read that some experts believe that the life span of a CD could range anywhere from 150-300 years. How do they know this? How and why would this degradation occur? What about 24K gold discs? What about DVD and other digital sources? Imagine someones 3'000 strong CD collection they loved so much suddenly becoming worthless in some historians archive! Of course, copies could be made on to newer discs, and we will all be long gone before this happens anyway, but that's not the point. How ironic it would be that some of yesterdays 78rpms may still be playing on after our discs of today give up their ghosts!</font>
 
Rob Babcock

Rob Babcock

Moderator
<font color='#8D38C9'>Lots of things can happen to a CD (or LP, for that matter). &nbsp;I once read about a problem in tropical locales where a certain bacteria actually &quot;eats&quot; vinyl- it can also cause damage to the polycarbonate layer of a CD, too.

Obviously a CD is susceptible to scratches, especially on the label side. &nbsp;Once the polycarbonate is breached, oxidation of the aluminum layer is inevitable. &nbsp;The aluminum layer upon which the pits are impressed will literally rot away. &nbsp;If you want to give yourself an ulcer, grab a stack of your oldest CDs sometimes and hold them up to a strong light- do you see any pinholes? &nbsp;Hopefully you don't, but I've found this on enough of my oldest discs to cause concern. &nbsp;The pinholes will get bigger over time until they compromise the integrity of the data; then it's &quot;game over&quot; for your disc. &nbsp;I've actually watched a few discs over the last few years and seen the problem worsen over time.

Some early discs seem to have a defect in the manufacturing process that allows air to reach the aluminum of the CD. &nbsp;I remember reading about a certain facility where the bulk of the &quot;rotting&quot; discs came from (wish I could recall the name). &nbsp;They were offering to replace the defective discs at one time.

Properly stored and cared for a pressed CD should last &quot;indefinately&quot;. &nbsp;The aluminum layer that stores the data does so on pits that are physically pressed into the disc by a glass master- in one sense, the guts of a CD are similar to that of an LP. &nbsp;If a thin layer of gold is used in place of aluminum the disc should be nearly impervious to the passing of time. &nbsp;

A CD-R is another matter, however. &nbsp;An organic dye in a semisolid crystaline form is partially melted by a laser; when it cools the pits are formed. &nbsp;This dye doesn't last forever, and it's particularly vulnerable to being broken down by strong light (like direct sunlight). &nbsp;Accelerated aging tests are performed by subjecting the discs to conditions far in excess of what they'd normally face, but it seems to me that no test could perfectly simulate the &quot;X factor&quot; of time itself, but I guess the tests are widely accepted. &nbsp;Mitsui (my favorite CD-R manufacturer) says their products will last over a century and claim a life expectantcy of over 300 years for their Archival Gold CD-Rs.

As you say, you could always make a copy of each disc every X amount of years. &nbsp;But this assumes that the CD format endures that long. &nbsp;It's had a good run, but DVD-R could well overtake it within a few years. &nbsp;You could transfer the music to a DVD-R (data is data) but inevitably the DVD-R will be replaced someday, too. &nbsp;Presumably you would keep transferring your stuff to each new format as it comes out.

It would be ironic if our &quot;perfect sound forever&quot; discs all rotted away within our lifetime. &nbsp;But I doubt they will. &nbsp;The format overall seems pretty durable. &nbsp;I've contemplated making a CD-R copy of every single disc I own (and discussed how to go about it at Audiocircle.com)- the idea would be to make a dupe of each one and stack them back into &quot;cakeboxes&quot; stored in my attic. &nbsp;I even toyed with the idea of keeping the spindles of recorded CD-Rs in my safe deposit box at my bank. &nbsp;This of course would give me some solace if my place was robbed or my collection was destroyed in a fire. &nbsp;It was pointed out to me also that it may be smarted to use the CD-R and keep the original tucked away, but I like having the art, liner notes, etc.</font>
 
A. Vivaldi

A. Vivaldi

Audioholic
<font color='#000000'>I'am the philosopher, but you are the wise man. You've answered those questions so well nobody else need bother. Just one question, what about DVDs? I've noticed they seem to be more sensitive then cds. Some DVDs that I rent won't play correctly even if there are only minor scuffs and scratchs, but a CD in much worse condition plays fine. Do you think they may not last as long?  <table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Quote </td></tr><tr><td id="QUOTE">Some early discs seem to have a defect in the manufacturing process that allows air to reach the aluminum of the CD.  I remember reading about a certain facility where the bulk of the &quot;rotting&quot; discs came from (wish I could recall the name).  They were offering to replace the defective discs at one time.
</td></tr></table>  I remember reading about some early classical CDs that had pin holes in them when brand new!<table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Quote </td></tr><tr><td id="QUOTE">As you say, you could always make a copy of each disc every X amount of years.  But this assumes that the CD format endures that long.  It's had a good run, but DVD-R could well overtake it within a few years.  You could transfer the music to a DVD-R (data is data) but inevitably the DVD-R will be replaced someday, too.  Presumably you would keep transferring your stuff to each new format as it comes out.
</td></tr></table>  Even though virtually no one listens to 78rpms anymore, there's still historians transfering them to CD using modern technology. I imagine there may be some in the future who will do the same thing with CD on whatever format they have. Imagine all the music or master tapes that may be completely forgotton about or lost in 150-300 years? (considering todays music, that may be a good thing!) They won't be able to however, if the CDs die out.<table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Quote </td></tr><tr><td id="QUOTE">It would be ironic if our &quot;perfect sound forever&quot; discs all rotted away within our lifetime.</td></tr></table>  I'm gonna be pissed when I'm 80 if my Highlander DVD craps out on me!
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Rob Babcock

Rob Babcock

Moderator
<font color='#8D38C9'>Highlander won't crap out you, you fool, it's immortal!
  Sorry, couldn't resist.  I dunno about DVDs- the pits are much smaller, so on one hand it would take less of a scratch to damage them.  But on the other hand, their error correction system is much more powerful and robust.  And since pit size aside a CD &amp; DVD utilize a very similar technology, I have to think the CD years have taught the disc makers enough about the problems &amp; their solutions that they don't have to reinvent the wheel.

So far all of my 400 disc DVD collection works perfectly, but the DVD has a lot easier time of it than a typical CD.  How many times will you watch a movie per year (okay, one that isn't &quot;Highlander&quot;
)?  Sure a Disney one might get spun twice a day for awhile, but inevitably the kiddies will tire of it and move on to the next.  Many movies in my collection have been watched only once (and a few not at all).  Contrast this with a CD- you might play you favorite disc a couple times a day, especially when you first get it and are getting to know it.  I shudder to think how many times the true classics in my collection get played (Priest, Maiden, XTC, Rush, Chris Isaak, Beach Boys, Johnny Cash).  Of course, I have a lot of CD-Rs of my favorite songs, too.  That probably saves some handling.

Likewise, back before I had a burner my CDs got played in the car a lot, and they got lent out and went to parties.  Lots of people didn't handle them as carefully as I did- and back when I bought my first player I was a junior in HS and I didn't really treat the discs with the care I could have.  In contrast, my movies never see a car or a disc changer.  I very rarely lend one out, and then only to one or two guys I trust with them.

Have you gone thru a sampling of your older discs, A. Vivaldi?  Maybe it's just my bad luck or the result of my youthful ignorance of proper disc care, but I have a fair number of pinholed discs.  Now that I'm aware of this problems, I'm seeing it routinely in CDs I get at the used disc stores, too.  A disc can be handled carefully, have no scratches, the art can be immaculate, yet you can hold it up to the sunlight and still see pinholes.  I'm not sure how serious this is or how long it will take to render a disc unplayable, but I'm convinced it's a problem.  

I'm curious to know if anyone else has seen much of this.  Once you know to start looking for it you often find it a lot more than you'd think.</font>
 
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H

hopjohn

Full Audioholic
<font color='#000000'>I have experienced problems with CD-R discs that were used in my car. One hot day a few summer's back my car's CD player wouldn't load a disc. I took it out to inspect it and about 75% of the playing side was discolored a dark brown color. I think it was more from heat than direct sunlight, but nonetheless it was destroyed. The cd had been in a small, black CD case resting in my car seat, and I wasn't using a sun shade or anything. I don't recall the CD-R being very warm when I put it in, but then again I was only holding the very edges.

I always make copies of CD's I listen to in my car for fear of it being broken into, which has happened in the past. It's much easier to replace a radio than a hundred or so CD's. As cheap as CD-R are nowadays it's a no brainer.</font>
 
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